The present invention relates to seals which are positioned against a moving surface, and more particularly to seals which prevent lubricant leakage from a bearing. The seal includes a conductor for indicating that the body of the seal has undergone excessive wear. The conductor is embedded within the body of the seal at a specified depth, namely the depth of acceptable wear. The electrical continuity of the conductor can be checked to determine if the seal body has worn to the specified depth.
Machinery often includes members which move with respect to each other. Bearings have long been used to facilitate such movement. Bearings are used to aid in transmitting forces from one member to another and to reduce friction. Rolling elements are often used in bearings to reduce friction, such as in ball bearings. Bearings often contain lubricant to reduce the friction created within the bearing.
Leakage of lubricant from bearings has long been a problem. Contamination of the bearings with foreign material such as dirt has also long been a problem. Both loss of lubricant and contamination lead to increased friction and wear within the bearing, damaging the bearing and perhaps damaging the machinery.
Seals composed of a soft polymeric material are used with bearings to prevent lubricant leakage and contamination. The polymeric material contacts a moving surface in the bearing and provides a seal. Friction between the polymeric material and the moving surface gradually wears the surface of the polymeric material away. If the polymeric material becomes too worn, it will no longer form a tight seal against the moving surface, and lubricant leakage from the bearing and contamination of the bearing again become problems.
Various methods have been developed to prevent or detect leakage past a seal. As shown in U.S. Pat. No. 4,761,023, one method involves monitoring the pressure of the fluid on the high pressure side of the seal, with a loss of pressure indicating leakage past the seal. Alternatively, as shown in U.S. Pat. No. 4,290,611, the fluid pressure on the low pressure side of the seal may be monitored, with an increase in pressure indicating lubricant leakage. A third method, such as that shown in U.S. Pat. No. 4,178,133, uses colored fluid and visual monitoring of leakage past a seal. Still other methods involve manual maintenance procedures, wherein seals are inspected or replaced on a regular basis.
These various methods to prevent or detect leakage past a seal have not proven satisfactory due to a number of problems. A problem with monitoring lubricant pressure is that it is only effective to detect leakage of the lubricant. Often this is too late to prevent damage. It is desired that the seal be replaced before leakage has begun. Similarly, visual monitoring of lubricant leakage can only indicate that leakage has begun, not that leakage is about to begin. A problem with manual inspection of a seal is that it requires an inspector who is not only trained but also diligent. Often seals are not inspected merely due to neglect or lack of diligence. Another problem with manual inspection is that it may require the machinery to be stopped during the inspection, which can be inconvenient. Scheduled seal replacement also has problems. Seals may wear more or less quickly depending on operating conditions, and scheduled seal replacement may occur too early (before the seal needs to be replaced) or too late (after the seal starts leaking).